package com.geostar.constructionland.attachment.util;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;

public class FileCharsetDetector {

  public static String detect(String sourceFilepath) {
    return detect(new File(sourceFilepath));
  }

  public static String detect(File sourceFile) {
    String charset = "GBK";
    byte[] first3Bytes = new byte[3];
    try {
      boolean checked = false;
      BufferedInputStream bis = new BufferedInputStream(new FileInputStream(sourceFile));
      bis.mark(0);
      int read = bis.read(first3Bytes, 0, 3);
      if (read == -1) {
        return charset; //文件编码为 ANSI
      } else if (first3Bytes[0] == (byte) 0xFF
          && first3Bytes[1] == (byte) 0xFE) {
        charset = "UTF-16LE"; //文件编码为 Unicode
        checked = true;
      } else if (first3Bytes[0] == (byte) 0xFE
          && first3Bytes[1] == (byte) 0xFF) {
        charset = "UTF-16BE"; //文件编码为 Unicode big endian
        checked = true;
      } else if (first3Bytes[0] == (byte) 0xEF
          && first3Bytes[1] == (byte) 0xBB
          && first3Bytes[2] == (byte) 0xBF) {
        charset = "UTF-8"; //文件编码为 UTF-8
        checked = true;
      }
      bis.reset();
      if (!checked) {
        int loc = 0;
        while ((read = bis.read()) != -1) {
          loc++;
          if (read >= 0xF0) {
            break;
          }
          if (0x80 <= read && read <= 0xBF) // 单独出现BF以下的，也算是GBK
          {
            break;
          }
          if (0xC0 <= read && read <= 0xDF) {
            read = bis.read();
            if (0x80 <= read && read <= 0xBF) // 双字节 (0xC0 - 0xDF)
            // (0x80
            // - 0xBF),也可能在GB编码内
            {
              continue;
            } else {
              break;
            }
          } else if (0xE0 <= read && read <= 0xEF) {// 也有可能出错，但是几率较小
            read = bis.read();
            if (0x80 <= read && read <= 0xBF) {
              read = bis.read();
              if (0x80 <= read && read <= 0xBF) {
                charset = "UTF-8";
                break;
              } else {
                break;
              }
            } else {
              break;
            }
          }
        }
      }
      bis.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
    return charset;
  }

}
